The purpose of this research is to: 1) Determine the bases for abnormal body surface (ECG) potentials and, 2) To determine mechanisms of common cardiac arrhythmias by recording multiple surface potentials, multiple simultaneous heart potentials and correlating both of these with the abnormal cardiac anatomy. In dogs and in patients, before and during cardiac surgery, record potentials from the body surface and from the epicardium, intramurally, endocardium, and Specialized Ventricular Conducting System (SVCS). These potentials are recorded for both normal rhythms and during transient arrhythmias which are spontaneous or evoked by cardiac stimulation. These studies demonstrate the fundamental variables which operate to generate the ECG and most cardiac arrhythmias. They also demonstrate that each problem is somewhat unique involving different weightings and interactions of the same fundamental variables. Using these methods, we have obtained information essental to proper interpretation of the ECG and for predicting the processes underlying certain cardiac arrhythmias. Already this information is being used to evaluate heart disease in patients and control certain cardiac rhythm disturbances. BIBLIOGRAPHIC REFERENCE: Walston, A., Boineau, J.P., Alexander, J.A., and Sealy, W.C.: Dissociation and delayed conduction in the canine right bundle branch. Circulation, 53:605-609, 1976.